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The purpose of this paper is to present the results of a five-month pilot testing program inTucson, Arizona to investigate the factors promoting nitrification and means of control. Twelveparallel pilot treatment trains each with plug-flow reactors were tested. The reactor systemsreproduced the nitrification process in a manner similar to nitrification events in full-scaledistribution systems. Previous laboratory studies supported by Tucson and full-scale systems inTexas have indicated that the presence of chlorite ion in water prevented the nitrification processand stabilized ammonia concentrations. These pilot studies confirmed the previous findings withchlorite ion and have opened new avenues of research for control of nitrification with minimaluse of additional chemicals. The following conclusions can be drawn from this study:plug flow reactors designed for this study successfully reproduced nitrification conditionsrepresentative of nitrification episodes in distribution systems;continuous chlorite ion feed prevented nitrification from ever getting established, evenat a concentration as low as 0.1 mg/L;in systems that already had serious nitrification underway, intermittent chlorite ion feedsas low as 0.2 mg/L stopped nitrification completely for several weeks after theirapplication;an intermittent dose of only 0.05 mg/L of chlorite ion damaged the ammonia oxidizingbacteria (AOB) population, which was able to re-establish itself in a few weeks, and a serialintermittent feed of 0.2 mg/L on the same reactor system badly damaged the AOB andeffectively stopped nitrification;in other pilot units studied, AOB regrowth was destroyed with an intermittent dose of 0.8mg/L; and,in full-scale distribution systems using chloramines, it appears that nitrification can beprevented by short-term and regularly scheduled applications of chlorite ion atconcentrations as low as 0.2 mg/L. Includes 8 references, tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 16File Size: 1 file , 1000 KB